According to a TEM (Transmission Electron Microscope), electron beams are applied to a sample and electron beams passed through the sample are magnified to form a TEM image. A TEM sample is formed to have a thickness, for example, of 0.05 to 0.4 μm so that electrons may pass therethrough. According to a STEM (Scanning Transmission Electron Microscope), focused electron beams are scanned over a sample and electron beams passed through the sample are detected to form a STEM image. Both TEM and STEM observations require a sample having a small thickness, which electron beams may pass through. Such observation methods have been utilized in a wide technical field including a semiconductor technology, since TEM and STEM observations provide a high resolution image.
In a semiconductor process, failure portions should be observed and analyzed to discover the cause. The failure of a semiconductor device includes foreign matters, open circuits and short circuits. Such failure portions cause of fabricating defective devices, and profits of manufacturing companies may be reduced. In order to improve the yield rate and reliability of semiconductor devices, observation and analysis is required. TEM observation and STEM observation are major and popular methods to find out failure portions of semiconductor devices. Such TEM and STEM may have analysis function to perform high resolution elementary analysis.
According to analysis using a TEM or STEM, including observation, elementary analysis and measurement, an observation surface (sampling surface) of a semiconductor wafer or semiconductor chip is observed. Such an observation is performed to a horizontal surface and a surface of a cross section. In order to create a cross section sample, a specific portion of a semiconductor device is mechanically exposed and is thin-film process is carried out by polishing and ion-thinning processes. Recently, a specific region of a semiconductor device (chip or wafer) is exposed and shaped to be thinner using FIB (Focused Ion Beam), for example, Ga ion beams having an accelerating energy of 30 kV.
A cross section sample created using FIB is observed by a SIM or SEM. In addition, for detailed analysis, a TEM observation is carried out to the same observation surface. A method described in Japanese Patent Publication 2003-194681A is applied to create a TEM sample, in which a sample is shaped to be thinner and the thin sample is extracted from a subject device by a micro manipulator.
Another method for creating TEM sample is described in Japanese Patent Publication No. 3,547,143, in which a sample is extracted from a subject device by a FIB process and is transferred to a sample holder by a mechanical probe. Then a thin-film process is carried out to the sample put on the sample holder.
When a TEM sample is formed or created using FIB after SIM observation or SEM observation, a material etched by Ga ion beams is deposited on an observation surface. Herein after, such a material deposited by an etching process is called “etching deposition”. If an etching deposition is deposited on the observation surface, the surface could not be observed by a TEM. An etching deposition can be removed by a FIB process, however, the observation surface would be also etched and removed unfavorably; and therefore, a different observation surface is exposed for the following TEM observation.